So far, as oral therapeutic drugs for diabetes mellitus, biguanide type and sulfonylurea type compounds have been used. However, with biguanide type compounds, lactic acidosis or hypoglycemia is caused and, with sulfonylurea type compounds, serious and prolonged hypoglycemia is caused, and the adverse effect thereof is posing a problem, hence the appearance of new therapeutic drug for diabetes mellitus without such defects is desired. It is also known that some of thiazolidine-2,4-dione derivatives exhibit hypoglycemic and lipid-lowering effects (Journal of Medicinal Chemistry, Vol. 35, P. 1853 (1992), Published Unexamined Patent Application No. Hei 1-272573), but, in all of these compounds, the substituted position of middle benzene ring that connects thiazolidine-2,4-dione ring and aromatic ring is p-position, or the middle benzene ring has no substituent, further the aromatic ring of the former is oxazol ring, the linkage of the latter is through sulfonamide, and the like, which differ structurally from compounds of the invention, N-benzyldioxothiazolidylbenzamide derivatives.
For the non-insulin dependent diabetes mellitus (NIDDM) accounting for the majority of diabetics, a blood sugar-lowering drug that improves the insulin resistance and has high safety and effectiveness is strongly desired.
As a result of diligent studies on a drug that improves the insulin resistance and has potent hypoglycemic effects and high safety, the inventors have found that novel N-benzyldioxothiazolidylbenzamide derivatives represented by a following general formula (1) have excellent hypoglycemic and lipid-lowering effects, leading to the completion of the invention.